MAIZE ROOT-DERIVED SOIL ORGANIC-CARBON ESTIMATED BY NATURAL C-13 ABUNDANCE

The natural enrichment of C-13 in maize plant material, compared to that of indigenous soil organic carbon, was used in the field to estimate the quantity of underground maize-derived C at harvest in October. Maize-derived C in the soil fractions coarser than 200-mu-m accounted for 12% of the C of the aboveground plant parts. Half of it was situated in the 20 cm wide x 20 cm deep soil portion situated beneath the plant. The soil fraction size-class 200-2000-mu-m contained 25% of the total and was the dominant size-class in the deeper layers. Because of the low resolution of the C-13 tracer, only a 95% confidence interval could be obtained for the quantity of solid material finer than 200-mu-m: between 1 and 9% of the aerial parts of maize. Contribution of maize-derived C to soil organic matter in early August was not significantly different from that at the harvest date.